Add test for #16943 and revert scanr good-producer-hood
The rewrite rules for scanr introduced to make it a good consumer (fixing #9355 (closed)) appear to cause scanr to be too strict in its list argument. This reverts the commit in question.
The rewrite rules for scanr introduced to make it a good consumer (fixing #9355 (closed)) appear to cause scanr to be too strict in its list argument. This reverts the commit in question.